A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator. A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present goals of hard disk drive design evolution. Further, the continuing evolution of HDDs has led to HDDs having thinner and thinner profiles. For example, the evolution of HDD profiles included 9.5 mm (height) HDDs, then 7 mm HDDs, and on to even thinner HDDs, while at the same time increasing the storage capacity and maintaining standard form factors (i.e., the “footprint” of an HDD) for installation in computing and data storage devices. Therefore, there are continuous design challenges associated with the evolution of HDDs to thinner profiles and more capacity, such as spatial challenges due to decreasing volumes within which to enclose HDD components. For example, in thinner mobile drives, especially in 2-disk models, there is not much design and performance margin with respect to spindle motor stiffness, such as in the context of shock and vibration robustness.
Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.